class Student_exercise():
    def __init__(self,order_id,student_id,problem_id,correct,end_time):
        self.order_id = order_id
        self.student_id = student_id
        self.problem_id = problem_id
        self.correct = correct
        self.end_time = end_time

    def tostring(self):
        return "order_id:{},student_id:{},problem_id:{},correct:{},endtime:{}".format(self.order_id,self.student_id,self.problem_id,self.correct,self.end_time)